Due to its broadly Anglophile stance, it attracted the support of many Unionists. Supporters of the former Irish Parliamentary Party were also a natural target group, given that the party's leader was the son of John Redmond, who had himself been leader of the nationalist party. A third group to which it sought to appeal, according to Manning (1972), comprised middle-class economic sectoral interests whose members were alienated by the policies of the Cumann na nGaedheal government, such as licensed vintners. These groups would not benefit from the more statist economic approach of the Fianna Fáil or Labour parties. However, all these efforts were largely ineffectual. The contemporary political scientist Warner Moss described the League as "a party of malcontents representing nothing fundamental in Irish political divisions."[1]

In the June 1927 general election, the National League won eight seats in the Dáil Éireann and entered opposition. In August, it supported Fianna Fáil's motion of no confidence in the Cumann na nGaedheal government in an attempt to form an alternative government under Labour leader Thomas Johnson, with the National League as the junior partner and Fianna Fáil supporting the resulting minority government. However, two League TDs opposed this tactic, Vincent Rice defecting to Cumann na nGaedheal and John Jinks, who was absent from the vote. As such, the motion failed, and the National League was portrayed as politically opportunist in its attempt at an alliance with two very different parties; National League supporters would have been far more likely to favour a continued Cumann na nGaedheal government than to allow the quasi-revolutionary Fianna Fáil to influence government policy.

The political discord associated with the Cumann na nGaedheal minority government prompted the September 1927 general election. Only two National League TDs, being Redmond and James Coburn, were elected. The financial strain of two general elections in four months took its toll on the small parties, and the National League declared bankruptcy in 1928. It was disbanded in 1931.